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United States Patent |
5,106,934
|
Wengrovius
,   et al.
|
April 21, 1992
|
Heat curable silicone compositions
Abstract
Heat curable silicone compositions are provided. Some of the heat curable
silicone compositions are convertible to silicone elastomers having a high
tear strength resulting from the employment of polydiorganosiloxane gum
having condensed organoalkenylsiloxy units, which is used in combination
with an organosilicon material having tetraorganodisilanoxy groups and a
Group VIII metal catalyst, such as platinum in elemental or chemically
combined form.
Inventors:
|
Wengrovius; Jeffrey H. (Scotia, NY);
Van Valkenburgh; Virginia M. (Albany, NY)
|
Assignee:
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General Electric Company (Schenectady, NY)
|
Appl. No.:
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518344 |
Filed:
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May 3, 1990 |
Current U.S. Class: |
528/15; 528/32; 528/37 |
Intern'l Class: |
C08G 077/06 |
Field of Search: |
528/15,32,37
|
References Cited
U.S. Patent Documents
4257936 | Mar., 1981 | Matsumoto et al. | 528/15.
|
4311739 | Jan., 1982 | Hardman et al. | 528/32.
|
4618666 | Oct., 1986 | Porte | 528/33.
|
4736048 | Apr., 1988 | Brown et al. | 528/37.
|
4975510 | Dec., 1990 | Wegehaupt et al. | 528/37.
|
Other References
Makoto Kumada et al., Synthesis of Some Methyldisilanes Containing
Functional Groups, J. Org. Chem. 1956, pp. 1264-1268, vol. 21.
Makoto Kumada et al., Preparation of Some Linear, Cyclic, or Cagelike
Methylsilicon Telomers Having a Framework of --SiSiO-- Chemical Abstract,
vol. 59.
|
Primary Examiner: Bleutge; John C.
Assistant Examiner: Hellender; Karen A.
Attorney, Agent or Firm: Teoli; William A., Davis, Jr.; James C., Webb, II; Paul R.
Claims
What is claimed is:
1. A heat curable silicone composition comprising by weight,
(a) 100 parts of an organopolysiloxane having a viscosity of at least 100
centipoise at 25.degree. C. and consisting essentially of condensed
diorganosiloxy units and 0.05 to 20 mole % of alkenylorganosiloxy units,
based on the total moles of condensed diorganoxiloxy units,
(b) 0.1 to 10 parts of an organosilicon material having chemically combined
tetraorganodisilanoxy groups of the formula,
##STR4##
where R is a member selected from the class consisting of the same or
different monovalent C.sub.(1-14) hydrocarbon radicals and monovalent
C.sub.(1-14) hydrocarbon radicals substituted with radicals inert during
equilibration or condensation and,
(c) an effective amount of a Group VIII metal catalyst in elemental or
chemically combined form.
2. A heat curable silicone rubber composition in accordance with claim 1,
where the organopolysiloxane is a polydiorganosiloxane gum consisting
essentially of chemically combined dimethylsiloxy units and
methylvinylsiloxy units.
3. A heat curable silicone composition in accordance with claim 1, where
the organosilicon material having chemically combined
tetraorganodisilanoxy groups is
##STR5##
4. A heat curable composition in accordance with claim 1, where the Group
VIII metal catalyst is a platinum catalyst.
5. A heat curable organopolysiloxane composition in accordance with claim
1, where the organosilicon material having chemically combined
tetraorganodisilanoxy groups is a hydrolyzate from a methylchlorosilane
reactor residue.
Description
CROSS REFERENCE TO RELATED APPLICATION
Reference is made to copending application, Ser. No. 07/433,814, filed Nov.
9, 1989, for Silicone Copolymers Having Tetraorganodisilyloxy Groups and
Intermediates Thereof.
The present invention relates to heat curable silicone compositions, such
as silicone rubber. More particularly, the present invention relates to
the employment of a polydiorganosiloxane gum having alkenyl radicals
attached to silicon, which is used in combination with an effective amount
of a Group VIII metal catalyst, such as a platinum, rhodium, ruthenium or
palladium catalyst and a minor amount of an organosilicon material
containing chemically combined tetraorganodisilanoxy groups of the
formula,
##STR1##
where R is a member selected from the class consisting of the same or
different monovalent C.sub.(1-14) hydrocarbon radicals and C.sub.(1-14)
hydrocarbon radicals substituted with monovalent radicals inert during
equilibration or condensation.
Prior to the present invention, a silicone cyclic having the formula,
##STR2##
referred to hereinafter as "D'.sub.2 " was reported by Kumada et al,
Journal of Organic Chemistry, 21, (1956), pp. 1264-68. Some linear, cyclic
or methylsilicon telomers having a framework of
##STR3##
are also reported by Kumada et al, Aogyo Kagaku Zasshi, 66 (5), 1963, pp.
637-41. As shown by Porte, U.S. Pat. No. 4,618,666, methylsilicon resins
having disilanoxy groups can be made by directly hydrolyzing
methylchlorosilane synthesis residue consisting essentially of
tetrachloro-1,2-dimethyldisilane, trimethyl-1,1,2-trichlorodisilane,
tetramethyl-1,2-dichlorodisilane and dimethyldichlorosilane. The resulting
methylsilicon resins have been found useful as molding powders, and as
textile and waterproofing agents used in building construction.
In copending application, Ser. No. 07/433,814, silicone copolymers are
shown, such as silicone polyimides, silicone polyamides, silicone
polyesters and silicone polycarbonates having condensed
tetraorganodisilanoxy groups of formula (1). A variety of heat and
electron beam curable silicone copolymers are provided which are silicone
polyimides, silicone polyamides, silicone polyesters, and silicone
polycarbonates having an M.sub.n from about 15,000 to about 30,000.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that heat curable
organopolysiloxane compositions are provided which can be converted to
high strength elastomers, if a polydiorganosiloxane gum consisting
essentially of condensed diorganosiloxy units and having chemically
combined alkenyl organosiloxy units, such as vinylmethylsiloxy units are
heated in the presence of an effective amount of a Group VIII transition
metal catalyst, such as a platinum, rhodium or ruthenium in elemental or
combined form, as defined hereinafter, and an organosilicon material
having chemically combined tetraorganodisilanoxy groups of formula (1).
STATEMENT OF THE INVENTION
There is provided by the present invention, a heat curable silicone
composition comprising by weight,
(A) 100 parts of an organopolysiloxane having a viscosity of at least 100
centipoise at 25.degree. C., and consisting essentially of condensed
diorganosiloxy units and having from 0.05 to 20 mole %, based on the total
moles of condensed diorganosiloxy units of alkenylorgahosiloxy units,
(B) 0.1 to 10 parts of an organosilicon material having chemically combined
tetraorganodisilanoxy groups of formula (1) and,
(C) an effective amount of a Group VIII metal catalyst in elemental or
chemically combined form.
Radicals included within R of formula (1) are, for example, C.sub.( 1-8)
alkyl radicals such as methyl, ethyl, propyl, butyl, pentyl; alkenyl
radicals such as vinyl, propenyl and cyclohexenyl; substituted alkyl
radicals such as trifluoropropyl, cyanoethyl and cyanopropyl; C.sub.(6-14)
aryl radicals such as phenyl, tolyl, xylyl, and halogenated derivatives
thereof, such as nitrophenyl and chlorophenyl.
Among the various organopolysiloxanes having condensed alkenyl
organosiloxane units there are included fluids and gums.
Organopolysiloxane gums having a viscosity of at least 100,000 centipoise
at 25.degree. C. are preferred and are preferably made by equilibrating
together organocyclopolysiloxane, such as octamethylcyclotetrasiloxane and
organoalkenylcyclopolysiloxane such as
tetravinyltetramethylcyclotetrasiloxane utilizing a standard equilibration
catalyst for example an acid treated clay or basic catalyst, such as KOH
or an alkaline silanolate. The silicone polymers can be further
equilibrated with a chainstopper such as a hexaorganodisiloxane, for
example hexamethyldisiloxane or 1,3 dialkenyltetraorganodisiloxane, for
example 1,3 divinyltetramethyldisiloxane. Depending upon the application
to which the heat curable silicone compositions are used, other
diorganosiloxanes can be used in the equilibration mixture to incorporate
into the silicone gums or fluids, other organosiloxane units, such as
cyanoalkylsiloxy units, such as methylcyanoethylsiloxy, methylsiloxy,
trifluoropropylsiloxy units, ethylphenylsiloxy units, and other
organosiloxy units if desired, by standard equilibration techniques.
The silicone gums can be reinforced with reinforcing fillers, such as fumed
silica, glass fibers, carbon fibers, and diatomaceous earth. There can be
utilized from about 0 to 500 parts of filler per 100 parts of silicone gum
by weight.
The Group VIII metal curing catalyst which can be employed in the practice
of the invention, include Group VIII metal previously identified in the
Background of the Invention, as well as iron, cobalt, nickel, iridium, and
osmium. The Group VIII catalyst can be used at from 5 ppm to 500 ppm of
catalyst, based on the total weight of the heat curable silicone
composition. There can be used elemental platinum, or platinum compounds
such as shown by Karstedt, U.S. Pat. Nos. 3,715,334 and 3,775,452.
Additional platinum complexes are shown by Ashby, U.S. Pat. No. 3,159,601
and Lamoreaux, U.S. Pat. No. 3,220,972. In addition to platinum, there
also can be used rhodium metal, or rhodium trichloride as well as
ruthenium dihalides or trihalides, such as the corresponding chlorides.
The Group VIII catalysts also can be used in combination with inhibitors ,
such as vinyl acetate, dimethyl maleate or diallyl maleate.
In order that those skilled in the art will be better able to practice the
present invention, the following examples are given by way of illustration
and not by way of limitation. All parts are by weight unless otherwise
indicated.
EXAMPLE 1
A series of heat cured silicone rubber compositions were prepared by
milling together 100 parts of a polydimethylsiloxane gum having a
penetration of about 900, and containing 2.5 parts of a methoxy stopped
polydimethylsiloxane process aid having a viscosity of about 10 centipoise
at 25.degree. C. and 2.5 parts of a silanol stopped polydimethylsiloxane
process aid having a viscosity of about 10 centipoise at 25.degree. C. and
0.8 part of vinyltriethoxysilane and about 63 parts of fumed silica
treated with octamethylcyclotetrasiloxane, and 50 parts ppm of platinum,
in the form of a vinyldisiloxane complex. The polydimethylsiloxane gum
also had 0.2 mole % of condensed methylvinylsiloxy units. The
aforementioned silicone rubber compositions were then blended with various
parts by weight of the silicone octamethylsilanoxy cyclic (D'.sub.2)of
formula (2). The silicone gum was initially blended on a two-roll mill
with the D'.sub.2 followed by the incorporation of the platinum catalyst.
The heat curable silicone rubber compositions were heated to 400.degree. F.
in a Monsanto Rheometer 100. The durometer, a measure of hardness
(inch-pound) was plotted as a function of time on a Monsanto
Therm-o-logger. A maximum durometer was observed in less than 2 minutes
and usually less than 1 minute. Durometer was also measured by the Shore A
method. The following durometers were obtained from the various heat cured
silicone rubber compositions expressed in parts of D'.sub.2.
______________________________________
D'.sub.2 (parts)
Durometer (in-pounds)
______________________________________
5 65
4 67
3 53
2 69
1 62
0.5 44
0.25 40
0 0
______________________________________
An uncured portion of each of the above compositions was retained at room
temperature for 60 days. None of the retained samples exhibited any
significant change in physical properties after the 60 days shelf period
under ambient conditions.
A portion of the heat cured silicone composition containing 2 parts of
D'.sub.2 was further evaluated for various physical properties after being
cured at 360.degree. F. in a Wabash Compression Molder. A heat curable
silicone composition also was prepared following the same procedure
utilizing the same fumed silica reinforced polydimethylsiloxane gum, but
substituting 1.2 parts of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane
(Lupersol 101, of the Pennwalt), Inc. for the platinum and D'.sub.2. The
respective heat cured rubbers provided the following physical properties,
______________________________________
D'.sub.2 /Pt
Peroxide
______________________________________
Tensile 1261 1116
Elongation 807 265
at break (%)
Tear strength 232 106
Durometer 51 71
______________________________________
The above results show that D'.sub.2 /Pt cured rubber has superior tensile
and tear strength when compared to the peroxide cured silicone rubber.
EXAMPLE 2
A vinyl chainstopped polydimethylsiloxane fluid having a viscosity of 400
centipoise at 25.degree. C. was prepared by equilibrating a mixture of
octamethylcyclotetrasiloxane, tetramethyl- tetravinylcyclotetrasiloxane
and 1,3-divinyltetramethyldisiloxane. The resulting polydimethylsiloxane
fluid also had about 4 mole % of vinylmethylsiloxy units based on the
total moles of condensed dimethylsiloxy units and methylvinylsiloxy units.
A disilanoxy containing hydrolysis product was obtained by hydrolyzing 20
grams of the primary chlorosilane residue obtained from a
methylchlorosilane reactor in 50 ml of water cooled in an ice bath. There
was added to the resulting mixture sufficient aqueous sodium hydroxide to
neutralize the HCl formed during the hydrolysis. Methyl orange was used to
indicate when the pH was neutral After stirring at 25.degree. C. for 12
hours, the mixture was extracted with hexane. The hexane solution was
filtered and dried over magnesium sulphate There was obtained 5 grams of a
disilanoxy hydrolyzate in the form of an oil after the solvent was removed
in vacuo A mixture of 50 parts of the vinyl chainstopped
polydimethylsiloxane fluid, 2.5 parts of the disilanoxy containing
hydrolyzate, and 50 ppm of platinum catalyst in the form of a platinum
vinylsiloxane complex was heated to 400.degree. F. for 2 minutes A cured
flexible product useful as an encapsulant was obtained.
Although the above examples are directed to only a few of the very many
variables which can be used in the practice of the present invention, it
should be understood that the present invention is directed to a much
broader variety of heat curable silicone compositions including silicone
elastomers as set forth in the description preceding these examples For
example, there can be used additional organosilicon materials containing
disilanoxy groups of formula (1) as well as other polydiorganosiloxane
gums and Group VIII curing catalyst.
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